1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus.
2. Description of the Related Art
An ultrasonic diagnostic apparatus generates an ultrasonic wave through its ultrasonic probe to allow it to propagate in a living body of a human subject, detects a corresponding echo at the probe and evaluates it for diagnostic purpose after being processed. Such a diagnostic examination by the ultrasound has been extensively utilized on the fetus of a pregnant woman. It is, therefore, necessary to fully check the safety of the apparatus in use.
With respect to the pulsed ultrasonic wave, the safety standard has been established based on the following various indexes:
Ispta (Spatial Peak Temporal Average Intensity)
Isppa (Spatial Peak Pulse Average Intensity)
Im (Maximum Intensity): the intensity of a wave of a maximum amplitude in one pulse
MI (Mechanical Index): the index of mechanical damage by physical energy generated upon the bursting of bubbles formed under a negative pressure of a given ultrasonic wave (longitudinal wave).
TI (Thermal Index): the index of thermal damage caused by the evolution of heat upon the absorption of a given ultrasonic wave during propagation in the living body of the human subject.
These are indexes recommended by the FDA of the U.S.A. The indexes Ispta, Isppa and Im have been conventionally used among the users but, in recent years, these are being replaced with the new indexes MI and TI. Now is the time for the existing indexes to be changed to the new indexes, thus sometimes causing some confusion among the users.
The ultrasonic diagnostic apparatus having a measure of safety against a possible confusion is disclosed in JPN PAT. APPLN. KOKOKU PUBLICATION NO. 4-25013, JPN PAT. APPLN. KOKAI PUBLICATION NOs. 4-156832, 2-84944, 4-352953 and 3-146043, JPN UTILITY MODEL APPLN KOKAI PUBLICATION NO. 63-120611, etc. Of these publications, some are directed to the technique of adjusting the output level of an ultrasonic wave by the user and some to the technique of numerically displaying, together with an ultrasonic image, the output level of that ultrasonic wave. In these techniques, after the setting of the output level of a given ultrasonic wave it has not been possible to cope with the change of those parameters on the various output levels of the ultrasonic wave, such as replacing a probe with another kind of probe, changing a mode to another mode, varying the position of a transmission focus and changing the rate frequency. Since, in this case, those unaltered parameters, other than those already set out above, are maintained at their initial levels, the resultant output level of a given ultrasonic wave is higher than the initial-value. Therefore, various problems have been arisen due to a risk so that a given ultrasonic wave exceeds an output level that an operator has designed, a too low output level of a ultrasonic wave and hence a resultant poor image quality, etc.